The presence of liquids, often laden with dirt, is critical in safety particularly, for a transparent substrate of the glazing type, especially one used in the transportation. The nonwetting property of a substrate can be categorized into omniphobic. Omniphobic substrate means oil (including organic liquids) and water repellent substrate. Usually, the contact angle of omniphobic surface is at least higher than 70° for hexadecane and 900 in the case of water in case of flat surface. The liquid tends to bead up and easily flow off the substrate, simply by gravity if the substrate is inclined, or under the effect of aerodynamic forces or mechanical motions (vibration and rocking) during operation of vehicle.
The benefit of incorporating an omniphobic coating of the invention on a substrate, especially a glass substrate, for this type of product is twofold. Firstly, it allows the water droplets to slide off vertical or inclined surfaces, especially under the effect of aerodynamic forces or mechanical motions, for example in the case of a moving vehicle. Secondly, these droplets, sliding off the substrate, cleanse the surface by incorporating dirt and carry this away. Especially, the visibility of glass substrates can be improved to a certain degree by dispensing windshield washer fluids or cleaning devices windshield wipers.
One of the problems arising with the greatest acuity in the field of omniphobic coatings is that of the mechanical abrasion of the omniphobic coating. This abrasion occurs to a greater or lesser extent during substrate cleaning operations, which are periodically necessary, in particular for restoring satisfactory vision through a transparent substrate. Thus, it has long been sought to minimize the gradual removal of the omniphobic coatings of the aforementioned types, this occurring in particular under the action of windshield wipers in the case of an automobile, airplane, boat/ship windshield. Such removal may moreover and additionally result from degradation by ultraviolet radiation.
Because of the problems outlined above, there is a need for improved omniphobic coatings.